1. Field of the Invention
The present invention relates to a bumper beam formed of a heat-treatable aluminum alloy extrusion, a bumper structure including the bumper beam and a pair of bumper stays joined to both end portions of the bumper beam, and a method for manufacturing the bumper beam.
2. Description of the Related Art
Japanese Patent Nos. 3465862 and 4111651 and Japanese Unexamined Patent Application Publication Nos. 7-25296 and 2003-118367 disclose the manufacture of automotive reinforcing members, such as door beams and bumper beams, that includes crushing an end region of an aluminum alloy extrusion, which is composed of a pair of opposing flanges and a plurality of webs coupled to the flanges, in a direction perpendicular to a surface of the flanges. Japanese Patent No. 4111651 discloses crushing of a press-quenched 6000 series (Al—Mg—Si) aluminum alloy extrusion after age hardening. Japanese Unexamined Patent Application Publication No. 2003-118367 discloses crushing of a press-quenched 6000 or 7000 series (Al—Zn—Mg) aluminum alloy extrusion during T1 tempering after extrusion, and age hardening of the extrusion after the crushing.
Even 7000 series aluminum alloy extrusions after press quenching and before age hardening (T1-tempered members) are hardened through natural aging and suffer a decrease in formability. As described in Japanese Unexamined Patent Application Publication Nos. 7-305151, 10-168553, and 2007-119853, in order to improve formability, 7000 series aluminum alloys hardened through natural aging are subjected to reversion treatment to decrease the strength thereof.
Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2010-502496 discloses annealing a longitudinal portion (a central portion, an end portion, or a joint for a bumper stay) of a cylindrical bumper beam manufactured by roll forming of a high-strength steel sheet to soften only the longitudinal portion and thereby improving the collision energy absorption characteristics.